Crucibwe steew is steew made by mewting pig iron (cast iron), iron, and sometimes steew, often awong wif sand, gwass, ashes, and oder fwuxes, in a crucibwe. In ancient times steew and iron were impossibwe to mewt using charcoaw or coaw fires, which couwd not produce temperatures high enough. However, pig iron, having a higher carbon content dus a wower mewting point, couwd be mewted, and by soaking wrought iron or steew in de wiqwid pig-iron for wong periods of time, de carbon content of de pig iron couwd be reduced as it swowwy diffused into de iron, uh-hah-hah-hah. Crucibwe steew of dis type was produced in Souf and Centraw Asia during de medievaw era. This generawwy produced a very hard steew, but awso a composite steew dat was inhomogeneous, consisting of a very high-carbon steew (formerwy de pig-iron) and a wower-carbon steew (formerwy de wrought iron). This often resuwted in an intricate pattern when de steew was forged, fiwed or powished, wif possibwy de most weww-known exampwes coming from de wootz steew used in Damascus swords. Due to de use of fwuxes de steew was often much higher in qwawity (wacking impurities) and in carbon content compared to oder medods of steew production of de time.

Techniqwes for production of high qwawity steew were devewoped by Benjamin Huntsman in Engwand in de 18f century. Huntsman used coke rader dan coaw or charcoaw, achieving temperatures high enough to mewt steew and dissowve iron, uh-hah-hah-hah. Huntsman's process differed from some of de wootz processes in dat it took a wonger time to mewt de steew and to coow it down and awwowed more time for de diffusion of carbon, uh-hah-hah-hah.[1] Huntsman's process used iron and steew as raw materiaws, in de form of bwister steew, rader dan direct conversion from cast iron as in puddwing or de water Bessemer process. The abiwity to fuwwy mewt de steew removed any inhomogeneities in de steew, awwowing de carbon to dissowve evenwy into de wiqwid steew and negating de prior need for extensive bwacksmiding in an attempt to achieve de same resuwt. Simiwarwy, it awwowed steew to simpwy be poured into mowds, or cast, for de first time. The homogeneous crystaw structure of dis cast steew improved its strengf and hardness compared to preceding forms of steew. The use of fwuxes awwowed nearwy compwete extraction of impurities from de wiqwid, which couwd den simpwy fwoat to de top for removaw. This produced de first steew of modern qwawity, providing a means of efficientwy changing excess wrought iron into usefuw steew. Huntsman's process greatwy increased de European output of qwawity steew suitabwe for use in items wike knives, toows, and machinery, hewping to pave de way for de Industriaw revowution.

Iron awwoys are most broadwy divided by deir carbon content: cast iron has 2-4% carbon impurities; wrought iron oxidizes away most of its carbon, to wess dan 0.1%. The much more vawuabwe steew has a dewicatewy intermediate carbon fraction, and its materiaw properties range according to de carbon percentage: high carbon steew is stronger but more brittwe dan wow carbon steew. Crucibwe steew seqwesters de raw input materiaws from de heat source, awwowing precise controw of carburization (raising) or oxidation (wowering carbon content). Fwuxes, such as wimestone, couwd be added to de crucibwe to remove or promote suwfur, siwicon, and oder impurities, furder awtering its materiaw qwawities.

Various medods were used to produce crucibwe steew. According to Iswamic texts such as aw-Tarsusi and Abu Rayhan Biruni, dree medods are described for indirect production of steew.[2] The medievaw Iswamic historian Abu Rayhan Biruni (c. 973–1050) provides de earwiest reference of de production of Damascus steew.[3] The first, and de most common, traditionaw medod is sowid state carburization of wrought iron. This is a diffusion process in which wrought iron is packed in crucibwes or a hearf wif charcoaw, den heated to promote diffusion of carbon into de iron to produce steew.[4] Carburization is de basis for de wootz process of steew.
The second medod is de decarburization of cast iron by removing carbon from de cast iron, uh-hah-hah-hah.[3]
The dird medod uses wrought iron and cast iron, uh-hah-hah-hah. In dis process, wrought iron and cast iron may be heated togeder in a crucibwe to produce steew by fusion, uh-hah-hah-hah.[4] In regard to dis medod Abu Rayhan Biruni states: "dis was de medod used in Hearf". It is proposed dat de Indian medod refers to Wootz carburization medod;[3] i.e., de Mysore or Tamiw processes.[5]

Variations of co-fusion process have been found primariwy in Persia and Centraw Asia but have awso been found in Hyderabad, India[6] cawwed Deccani or Hyderabad process.[5] For de carbon, a variety of organic materiaws are specified by de contemporary Iswamic audorities, incwuding pomegranate rinds, acorns, fruit skins wike orange peew, weaves as weww as de white of egg and shewws. Swivers of wood are mentioned in some of de Indian sources, but significantwy none of de sources mention charcoaw.[7]

Crucibwe steew is generawwy attributed to production centres in India and Sri Lanka where it was produced using de so-cawwed "wootz" process, and it is assumed dat its appearance in oder wocations was due to wong distance trade.[8] Onwy recentwy it has become apparent dat pwaces in Centraw Asia wike Merv in Turkmenistan and Akhsiket in Uzbekistan were important centres of production of crucibwe steew.[9] The Centraw Asian finds are aww from excavations and date from de 8f to 12f centuries CE, whiwe de Indian/Sri Lankan materiaw is as earwy as 300 BCE. In addition, India's iron ore had trace vanadium and oder awwoying ewements weading to increased hardenabiwity in Indian crucibwe steew which was famous droughout de middwe east for its abiwity to retain an edge.

Whiwe crucibwe steew is more attributed to de Middwe East in earwy times, dere have been swords discovered in Europe, particuwarwy in Scandinavia. The swords in qwestion have de ambiguous name inwaid into it, Uwfberht. These swords actuawwy date to a 200-year period from de 9f century to de earwy 11f century. It is specuwated by many[who?] dat de process of making de bwades originated in de Middwe East and subseqwentwy been traded during de Vowga Trade Route days.[10]

In de first centuries of de Iswamic period, dere appear some scientific studies on swords and steew. The best known of dese are by Jabir ibn Hayyan 8f century, aw-Kindi 9f century, Aw-Biruni in de earwy 11f century, aw-Tarsusi in de wate 12f century, and Fakhr-i-Mudabbir 13f century. Any of dese contains far more information about Indian and damascene steews dan appears in de entire surviving witerature of cwassicaw Greece and Rome.[11]

There are many ednographic accounts of Indian crucibwe steew production, however, scientific investigations of crucibwe steew remains have onwy been pubwished from four regions: dree in India and one in Sri Lanka.[12] Indian/Sri Lankan crucibwe steew is commonwy referred to as wootz, which is generawwy agreed to be an Engwish corruption of de word ukko or hookoo.[13] European accounts from de 17f century onwards have referred to de repute and manufacture of ‘wootz’, a traditionaw crucibwe steew made speciawwy in parts of soudern India in de former provinces of Gowconda, Mysore and Sawem. As yet de scawe of excavations and surface surveys is too wimited to wink de witerary accounts to archaeometawwurgicaw evidence.[14]

The known sites of crucibwe steew production in souf India, i.e. at Konasamudram and Gatihosahawwi, date from at weast de wate medievaw period, 16f century.[15] One of de earwiest known sites, which shows some promising prewiminary evidence dat may be winked to ferrous crucibwe processes in Kodumanaw, near Coimbatore in Tamiw Nadu.[16] The site is dated between de dird century BCE and de dird century CE.[17] By de seventeenf century de main centre of crucibwe steew production seems to have been in Hyderabad. The process was apparentwy qwite different from dat recorded ewsewhere.[18] Wootz from Hyderabad or de Decanni process for making watered bwades invowved a co-fusion of two different kinds of iron: one was wow in carbon and de oder was a high-carbon steew or cast iron, uh-hah-hah-hah.[19]Wootz steew was widewy exported and traded droughout ancient Europe, China, de Arab worwd, and became particuwarwy famous in de Middwe East, where it became known as Damascus steew.[20][21]

Recent archaeowogicaw investigations have suggested dat Sri Lanka awso supported innovative technowogies for iron and steew production in antiqwity.[22] The Sri Lankan system of crucibwe steew making was partiawwy independent of de various Indian and Middwe Eastern systems.[23] Their medod was someding simiwar to de medod of carburization of wrought iron, uh-hah-hah-hah.[22] The earwiest confirmed crucibwe steew site is wocated in de knuckwes range in de nordern area of de Centraw Highwands of Sri Lanka dated to 6f −10f centuries CE.[24] In twewff century de wand of Serendib (Sri Lanka) seems to have been de main suppwier of crucibwe steew, but over de centuries swipped back, and by de nineteenf century just a smaww industry survived in de Bawangoda district of de centraw soudern highwands.[25]

A series of excavations at Samanawawewa indicated de unexpected and previouswy unknown technowogy of west-facing smewting sites, which are different types of steew production, uh-hah-hah-hah.[22][26] These furnaces were used for direct smewting to steew.[27] Because of deir wocation on de western sides of hiwwtops for use of wind in de smewting process dey are named west-facing.[28] Sri Lankan furnace steews were known and traded between de 9f and 11f centuries and earwier, but apparentwy not water.[29] These sites were dated to de 7f–11f centuries. The coincidence of dis dating wif de 9f century Iswamic reference to Sarandib[28] is of great importance. The crucibwe process existed in India at de same time dat de west- facing technowogy was operating in Sri Lanka.[30]

Centraw Asia has a rich history of crucibwe steew production, beginning during de wate 1st miwwennium CE.[31] From de sites in modern Uzbekistan and Merv in Turkmenistan, dere exists good archaeowogicaw evidence for de warge scawe production of crucibwe steew.[32] They aww bewong in broad terms to de same earwy medievaw period between de wate 8f or earwy 9f and de wate 12f century CE[33] Contemporary wif de earwy crusades.[32]

The two most prominent crucibwe steew sites in eastern Uzbekistan carrying de Ferghana Process are Akhsiket and Pap in de Ferghana Vawwey, whose position widin de Great Siwk Road has been historicawwy and archaeowogicawwy proved.[34] The materiaw evidence of de sites consists of warge number of archaeowogicaw finds rewating to steew making from 9f–12f centuries CE in de form of hundreds of dousands of fragments of crucibwes often wif massive swag cakes.[31] Archaeowogicaw work at Akhsiket, has identified dat de crucibwe steew process was of de carburization of iron metaw.[7] This process appears to be typicaw of and restricted to de Ferghana Vawwey in eastern Uzbekistan, and it is derefore cawwed de Ferghana Process.[35] This process wasts in dat region for roughwy four centuries..

Evidences of de production of crucibwe steew have been found in Merv, Turkmenistan, a major city on de 'Siwk Road'. The Iswamic schowar, aw-Kindi (CE 801–866) mentions dat during de ninf century de region of Khorasan, de area to which de cities Nishapur, Merv, Herat and Bawkh bewong, is a steew manufacturing centre.[36] Evidence from a metawwurgicaw workshop at Merv, dated to de ninf- earwy tenf century CE, provides an iwwustration of de co-fusion medod of steew production in crucibwes, about 1000 years earwier dan de distinctwy different wootz process.[37] The crucibwe steew process at Merv might be seen as technowogicawwy rewated to what Bronson (1986, 43) cawws Heyderabad process, a variation of de wootz process, after de wocation of de process documented by Voysey in de 1820s.[38]

The first European references to crucibwe steew seem to be no earwier dan de Post Medievaw period.[39] European experiments wif “Damascus” steews go back to at weast de sixteenf century, but it was not untiw de 1790s dat waboratory researchers began to work wif steews dat were specificawwy known to be Indian/wootz.[40] At dis time, Europeans knew of India's abiwity to make crucibwe steew from reports brought back by travewwers who had observed de process at severaw pwaces in soudern India.

From de mid-17f century onwards, dere are numerous vivid eyewitness accounts of de production of steew by European travewwers to de Indian subcontinent. These incwude accounts by Jean Baptist Tavernier in 1679, Francis Buchanan in 1807, and H.W. Voysey in 1832.[41]
The 18f, 19f and earwy 20f century saw a heady period of European interest in trying to understand de nature and properties of wootz steew. Indian wootz engaged de attention of some of de best-known scientists.[42] One was Michaew Faraday who was fascinated by wootz steew. It was probabwy de investigations of George Pearson in 1795 reported at de Royaw Society, which had de most far-reaching impact in terms of kindwing interest in wootz amongst European scientists.[43] He was de first of dese scientists to pubwish his resuwts and, incidentawwy, de first to use de word "wootz" in print.[44]

Anoder investigator, David Mushet, was abwe to infer dat wootz was made by fusion, uh-hah-hah-hah.[45] David Mushet patented his process in 1800.[46] He made his report in 1805.[44] But de first successfuw European process had been devewoped by Benjamin Huntsman some 50 years previouswy in de 1740s.[47]

Benjamin Huntsman was a cwockmaker in search of a better steew for cwock springs. In Handsworf near Sheffiewd, he began producing steew in 1740 after years of experimenting in secret. Huntsman's system used a coke-fired furnace capabwe of reaching 1,600 °C, into which up to twewve cway crucibwes, each capabwe of howding about 15 kg of iron, were pwaced. When de crucibwes or "pots" were white-hot, dey were charged wif wumps of bwister steew, an awwoy of iron and carbon produced by de cementation process, and a fwux to hewp remove impurities. The pots were removed after about 3 hours in de furnace, impurities in de form of swag skimmed off, and de mowten steew poured into mouwds to end up as castingots.[48][49] Compwete mewting of de steew produced a highwy uniform crystaw structure upon coowing, which gave de metaw increased tensiwe strengf and hardness compared to oder steews being made at de time.

Before de introduction of Huntsman's techniqwe, Sheffiewd produced about 200 tonnes of steew per year from Swedish wrought iron (see Oregrounds iron). The introduction of Huntsman's techniqwe changed dis radicawwy: one hundred years water de amount had risen to over 80,000 tonnes per year, or awmost hawf of Europe's totaw production, uh-hah-hah-hah. Sheffiewd devewoped from a smaww township into one of Europe's weading industriaw cities.

The steew was produced in speciawised workshops cawwed 'crucibwe furnaces', which consisted of a workshop at ground wevew and a subterranean cewwar. The furnace buiwdings varied in size and architecturaw stywe, growing in size towards de watter part of de 19f century as technowogicaw devewopments enabwed muwtipwe pots to be "fired" at once, using gas as a heating fuew. Each workshop had a series of standard features, such as rows of mewting howes, teaming pits,[cwarification needed] roof vents, rows of shewving for de crucibwe pots and anneawing furnaces to prepare each pot before firing. Anciwwary rooms for weighing each charge and for de manufacture of de cway crucibwes were eider attached to de workshop, or wocated widin de cewwar compwex. The steew, originawwy intended for making cwock springs, was water used in oder appwications such as scissors, axes and swords.

Previous to Huntsman, de most common medod of producing steew was de manufacture of shear steew. In dis medod, bwister steew produced by cementation was used, which consisted of a core of wrought iron surrounded by a sheww of very high-carbon steew, typicawwy ranging from 1.5 to 2.0% carbon, uh-hah-hah-hah. To hewp homogenize de steew, it was pounded into fwat pwates, which were stacked and forge wewded togeder. This produced steew wif awternating wayers of steew and iron, uh-hah-hah-hah. The resuwting biwwet couwd den be hammered fwat, cut into pwates, which were stacked and wewded again, dinning and compounding de wayers, and evening out de carbon more as it swowwy diffused out of de high-carbon steew into de wower-carbon iron, uh-hah-hah-hah. However, de more de steew was heated and worked; de more it tended to decarburize, and dis outward diffusion occurs much faster dan de inward diffusion between wayers. Thus, furder attempts to homogenize de steew resuwted in a carbon content too wow for use in items wike springs, cutwery, swords, or toows. Therefore, steew intended for use in such items, especiawwy toows, was stiww being made primariwy by de swow and arduous bwoomery process in very smaww amounts and at high cost, which, awbeit better, had to be manuawwy separated from de wrought iron and was stiww impossibwe to fuwwy homogenize in de sowid state.

Huntsman's process was de first to produce a fuwwy homogeneous steew. Unwike previous medods of steew production, de Huntsman process was de first to fuwwy mewt de steew, awwowing de fuww diffusion of carbon droughout de wiqwid. Wif de use of fwuxes it awso awwowed de removaw of most impurities, producing de first steew of modern qwawity. Due to carbon's high mewting point (nearwy tripwe dat of steew) and its tendency to oxidize (burn) at high temperatures, it cannot usuawwy be added directwy to mowten steew. However, by adding wrought iron or pig iron, awwowing it to dissowve into de wiqwid, de carbon content couwd be carefuwwy reguwated (in a way simiwar to Asian crucibwe-steews but widout de stark inhomogeneities indicative of dose steews). Anoder benefit was dat it awwowed oder ewements to be awwoyed wif de steew. Huntsman was one of de first to begin experimenting wif de addition of awwoying agents wike manganese to hewp remove impurities such as oxygen from de steew. His process was water used by many oders, such as Robert Hadfiewd and Robert Forester Mushet, to produce de first awwoy steews wike mangawwoy, high-speed steew, and stainwess steew.

Due to variations in de carbon content of de bwister steew, de carbon steew produced couwd vary in carbon content between crucibwes by as much as 0.18%, but on average produced a eutectoid steew containing ~ 0.79% carbon, uh-hah-hah-hah. Due to de qwawity and high hardenabiwity of de steew, it was qwickwy adopted for de manufacture of toow steew, machine toows, cutwery, and many oder items. Because no oxygen was bwown drough de steew, it exceeded Bessemer steew in bof qwawity and hardenabiwity, so Huntsman's process was used for manufacturing toow steew untiw better medods, utiwizing an ewectric arc, were devewoped in de earwy 20f century.[50][51]

In anoder medod, devewoped in de United States in de 1880s, iron and carbon were mewted togeder directwy to produce crucibwe steew.[52] Throughout de 19f century and into de 1920s a warge amount of crucibwe steew was directed into de production of cutting toows, where it was cawwed toow steew.

Anoder form of crucibwe steew was devewoped in 1837 by de Russian engineer, Pavew Anosov. His techniqwe rewied wess on de heating and coowing, and more on de qwenching process of rapidwy coowing de mowten steew when de right crystaw structure had formed widin, uh-hah-hah-hah. He cawwed his steew buwat; its secret died wif him. In de United States crucibwe steew was pioneered by Wiwwiam Metcawf.